docs: Fix a few typos

[timgates42]

There are small typos in:

• posts/conferences/bosc2018_day1a.md
• posts/seminars/tumor_heterogeneity_carter.md

Fixes:

• Should read suppressors rather than supressors.
• Should read service rather than serivce.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md

[chapmanb]

So sorry for missing this, I really apprecite the fixes.